The present invention relates to a method to perform central control to a line terminator and an element controller that are realizing such a method and to a tree-like network.
Such a tree-like network is already known in the art e.g. from The published European Patent Application, published at 26.03.1997, with the title “Arrangement for amplifying and combining optical signals, and method for upstream transmission realized therewith” with publication number EP 0 765 045 A1. Therein a tree-like optical network is described. The tree-like network consists of the upstream cascade connection of dedicated branches, a combiner arrangement and a common branch whereby a plurality of network units, called hereafter network terminators are coupled to a line terminator.
A so called grant is distributed by the line terminator to the different network terminators in order to permit one or more network terminators to react on the grant, according to an identification included in the grant ant to transmit an upstream burst also called upstream information signal.
Indeed, it is described by the Telecommunication Standardization Sector of ITU International Telecommunication Union in the G.983.1 standard of 10/98 with title “Series G: Transmission Systems and media, Digital Systems and Networks: Digital sections and digital line systems—Optical line systems for local and access networks: Broadband Optical Access Systems Based On Passive Optical Networks (PON)” at page 6, paragraph 4 of Definitions that an optical line terminator controls each upstream transmission from the optical network units by sending a permission. A grant, also called a permit, is a permission to transmit an upstream cell of an optical network terminator when an optical network terminator receives its own grant. Furthermore at paragraph 8.3.5.3.5. Grants, pages 36 to 37, the different types of grants are described.
As it is described in the above mentioned application, at the first column, lines 23 to 31, these known networks are demanding optical amplifiers in the dedicated branches in order to support the required optical power-budget. Furthermore at lines 49 to 52 it is described that also optical switches are required in these branches. The “in-line elements” that are used in the claims of the present application are e.g. such an optical amplifier or an optical switch. Indeed, these elements are included along the downstream transmission path of the downstream information signals distributed by the line terminator to the plurality of network terminators and along the upstream transmission path of the upstream information signals being transmitted by one of the network terminators.
These in-line elements must perform predefined functions at predefined time moments. In this way a semiconductor optical amplifier e.g. an integration of such an optical amplifier and an optical switch needs to be switched on/off at predefined time moments and needs to set a predefined gain at other predefined time moments. Another in-line element is a burst mode receiver being coupled on the common branch to the line terminator. It has to be remarked that in the event when the tree-like network is an optical tree-like network such a burst mode receiver is usually included in the optical line terminator and coupled to the electrical line terminator. The burst mode receiver must detect at predefined time moments certain activity form the network terminators and needs to perform at other predefined time moments automatic gain control for the different network terminators.
It is also described in the referred application that a possible way to control the optical switches by the line terminator i.e. on/off instruction is realized by capturing downstream grant information being downstream transmitted by the line terminator to the network terminators. Although that this grant information, that includes as described in the above mentioned standard the network terminator identification, is used to determine whether an upstream information signal will be present or will not be present during a predetermined time interval for a particular optical switch, i.e. during normal operation mode of a network terminator, such a method is not sufficient to perform a total control of all the in-line elements during e.g. a preparation phase of the network terminators and other network elements.
In order to perform the required functionality's by these in-line elements at the predefined time moments different approaches are possible. Indeed a possible method is e.g. a central control performed by the line terminator with transmission of control signals between the line terminator and the in-line elements. However, in networks with high splitting factor and many different in-line elements such a solution would require many additional control signals and extra overhead.